Answer: Toxic megacolon secondary to Clostridium difficile colitis.
- Toxic megacolon is acute fulminant transmural pancolitis resulting in a markedly dilated, non-obstructed adynamic colon with air-fluid levels, in the setting of sepsis. This is a potentially life-threatening condition if not diagnosed promptly and managed appropriately.
- Causes of toxic megacolon include inflammatory processes such as ulcerative colitis (most commonly) or infectious colitis, including pseudomembraneous colitis, which this patient had. (Infectious agents include bacteria such as C. difficile, Salmonella, Shigella and Campylobacter; viruses like CMV; and parasites such as E. histolytica and Cryptosporidium.)
- The pathophysiology of toxic megacolon is not entirely clear. Inflammation in toxic megacolon is transmural, such that inflammation of the smooth muscle layer of the colon can lead to dilatation. Mucosal inflammation may lead to the release of inflammatory mediators, including nitric oxide (which inhibits smooth muscle tone), leading to colonic dilatation. A few of the identified precipitating factors include antimotility agents, opiate use, anticholinergics, cessation of steroid use, barium enema and colonoscopy.
- Patients typically present with abdominal distention, diarrhea, and abdominal pain. This patient presented primarily with complaints of abdominal distension, diarrhea and altered mental status, but not so much of pain. One study done by Trudel in 1995 demostrated that of patients with C. difficile colitis and toxic megacolon, diarrhea was a complaint in 100% of cases, malaise in 91%, and abdominal pain and distention in 82%. Physical exam findings are of a septic picture—tachycardia, fever, altered mental status, and postural hypotension. The development of peritoneal signs may herald one of the more serious potential complications of toxic megacolon, perforation.
- The diagnosis of toxic megacolon is a clinical diagnosis in the setting of positive radiographic findings of colonic distension, as described in the case above. The radiographic guideline for megacolon generally is of dilatation greater than 6 cm on abdominal radiographs, although the overall clinical picture supercedes absolute diameter of the colon. Additional findings on CT include irregular contours of the bowel wall, absent or distorted haustra, and, in more ominous cases, mesenteric abcess, free air, or vascular compromise. Thickening of the bowel wall, as was seen on this study, is a very sensitive sign of toxic megacolon due to C. difficile colitis.
- Treatment of toxic megacolon depends on severity of the clinical picture and the causative agent. In this case, the patient was found to be septic on workup, with lactic acidosis, sever and was taken to the operating room for exploratory laparotomy. A sub-total colectomy and iliostomy was performed to remove a large, dilated, edematous portion of colon. The patient subsequently did well, and was discharged several days later.
- Gan SI, Beck PL. A new look at toxic megacolon: an update and review of incidence, etiology, pathogenesis, and management. Am J Gastroenterol 2003; 98:2363.
- Kawamoto S, Horton K and Fishman E. Pseudomembranous Colitis: Spectrum of Imaging Findings with Clinical and Pathologic Correlation. July 1999 RadioGraphics, 19, 887-897.
- Mukai JK, Janower ML. Diagnosis of pseudomembranous colitis by computed tomography: a report of two patients. Can Assoc Radiol J. 1987;38(1):62.
- Rogeveen et al. Ulcerative colitis. May 2006 RadioGraphics, 26, 947-951.
- Thoeni RF and Cello JP. CT imaging of colitis. September 2006 Radiology, 240, 623-638.
- Trudel JL, Deschenes M, Mayrand S, Barkun AN. Toxic megacolon complicating pseudomembranous enterocolitis. Dis Colon Rectum. 1995;38(10):1033.
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